This invention relates to commercial sterilization of meat and meat products by altering the character of the meat surface. More particularly, this invention relates to a method of combining ultra-high temperature pasteurization and electron beam radiation to produce commercially sterile raw meat and meat products that may be stored without refrigeration. Only the surface or visible portion is altered with the remainder of the deep muscle tissue below about 2 mm remaining in its raw or unaltered state except for the destruction of microorganisms.
Extending the storage life of meat and meat products has been a subject of mankind's ingenuity since before recorded history. Many procedures have been developed, but they are all subject to certain limitations. Cooking, smoking, and curing all render meat less susceptible to spoilage, but the flavor of the meat is altered, sometimes drastically, and the meat is still subject to eventual spoilage. Chemical additives may be effective preservatives, but commercial acceptance and regulatory approval have been limiting factors. Meat can be frozen and stored for extended periods of time without seriously affecting flavor or palatability, but maintaining the meat in a frozen state is expensive.
Consumers discriminate against fresh beef steaks that contain more than about 25% surface discoloration. D. Hood & E. Riordan, 8 J. Food Technol. 333 (1973). Surface discoloration of 50-75% is evident in fresh beef steaks after 4 days of retail display using primal cut packaging/precutting treatments. M. Miller et al., 50 J. Food Sci. 1544 (1985). Cutting subprimals into steaks, followed by vacuum packaging tends to decrease retail case life, juiciness, and tenderness. Retail fresh meat establishments have very few alternatives when disposing of discolored higher priced cuts except reducing price, retrimming, and grinding, all of which involve loss of value. Similarly, vacuum-packaged primal beef cuts lose quality after 45-60 days of storage depending on the storage temperature, degree of evacuation, permeability of the packaging material, initial load, and composition of the primal. S. Seideman et al., 39 J. Milk Food Technol. 745 (1976); S. Seideman et al., 41 J. Food Sci. 738 (1976). Since the loss of bloom and the growth of microorganisms (assuming internal muscle sterility) are both primarily surface phenomena, the application of technology to improve the appearance of the surface and control microbial growth would be beneficial to extending shelf life.
Methods of sterilizing meat and other animal tissues with high temperature treatment have been described previously. U.S. Pat. No. 4,539,212 to Hunter teaches a process for sterilizing low-acid food containing meat or textured vegetable protein by acidifying the food, heating at high temperature (104.degree.-137.degree. C.) for a short time (5-60 seconds), and packing with a hot-fill-and-hold procedure. U.S. Pat. No. 4,572,839 to Guitteny et al. teaches a method of high temperature sterilization of animal protein by grinding the raw material to make a slurry, partially hydrolyzing it, and heating a thin layer of the slurry to about 120.degree.-150.degree. C. for about 3 seconds to 15 minutes. U.S. Pat. No. 4,675,202 to Wenger et al. discloses a method of sterilizing a slurry containing egg yolks by acidifying and then heating at temperatures between 128.degree.-155.degree. C. for a period of 1-50 seconds. U.S. Pat. No. 4,201,796 to Harkins discloses a method of cooking meat by searing the surface of a cut or patty of meat by brief exposure to a blow torch pencil burner while leaving the inside of the meat relatively raw, refrigerating or freezing the meat, and cooking thoroughly in a microwave oven.
Methods for sterilizing and preserving food products with electron beam technology have also been described. U.S. Pat. No. 2,456,909 to Brasch discloses a method of sterilizing various types of meat including beef, pork, chicken, calf liver, and oysters with electron beam radiation. The method involves placing the food to be sterilized in a container and removing air by introducing an inert gas or evacuating the container, sealing the container air tight, freezing the food at -20.degree. C. to -100.degree. C., and irradiating the food with 3 to 6 MeV of high speed electrons during a series of consecutive very short time periods, each lasting less 10.sup.-4 of a second. Brasch found it necessary to freeze the food to avoid changes in taste, odor, appearance, and structure due to unwanted side reactions such as formation of hydrogen peroxide, ozone, nitrous oxides, mercaptans, and sulfides; denaturation of proteins; decarboxylation; and hydrolysis. U.S. Pat. No. 3,876,373 to Glyptis discloses electron beam sterilization as a prior art sterilization method, but rejected it for reasons of safety, expense, and alteration of the taste and color of the food.
Preservation of food by exposure to ionizing radiation has also been described, such as in U.S. Pat. No. 3,567,462 to Silverman et al., which shows a method for extending the storage life of fresh animal tissue by pasteurizing the tissue by exposure to radiation and storing at refrigerated temperatures (0.degree.-7.2.degree. C.) in an atmosphere of 30-100% CO.sub.2.
In view of the foregoing, it will be appreciated that providing a method for sterilizing meat and meat products on a commercial scale that eliminates the need to refrigerate meat would be a significant advancement in the art.
Another significant advancement in the art would be to provide a method of reducing the cost of aging meat.
A further advancement in the art would be providing meat that is pathogen free, attractive in appearance, and ready for cooking in a microwave oven. Related to this would be providing a method for increasing the value of discolored retail cuts of meat. Still another advancement in the art would be to seal the surface of a cut of meat to inhibit dehydration and to enhance even heat distribution upon cooking in a microwave oven, and to improve the flavor of meat cooked in a microwave oven.